linux-kernel - [PATCH v3 2/2] sched: fix update NOHZ

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Message-Id: <1360346718-3313-3-git-send-email-vincent.guittot@linaro.org>
Date:	Fri,  8 Feb 2013 19:05:18 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	peterz@...radead.org, mingo@...nel.org, fweisbec@...il.com,
	rostedt@...dmis.org, efault@....de
Cc:	Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v3 2/2] sched: fix update NOHZ_IDLE flag

The function nohz_kick_needed modifies NOHZ_IDLE flag that is used to update
the nr_busy_cpus of the sched_group.
When the sched_domain are updated (during the boot or because of the unplug of
a CPUs as an example) a null_domain is attached to CPUs. We have to test
likely(!on_null_domain(cpu) first in order to detect such intialization step
and to not modify the NOHZ_IDLE flag

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eea870..dac2edf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5695,7 +5695,7 @@ void trigger_load_balance(struct rq *rq, int cpu)
 	    likely(!on_null_domain(cpu)))
 		raise_softirq(SCHED_SOFTIRQ);
 #ifdef CONFIG_NO_HZ
-	if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
+	if (likely(!on_null_domain(cpu)) && nohz_kick_needed(rq, cpu))
 		nohz_balancer_kick(cpu);
 #endif
 }
-- 
1.7.9.5

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